Can any Democrat hold the White House for a third term?

Confetti flies at the 2012 Democratic National Convention. (Los Angeles Times )

Does Hillary Clinton -- or any Democratic candidate -- really face an uphill battle in the presidential election of 2016?

In my Wednesday column, I noted that in the six most recent presidential elections with no incumbent in the race, if one party has been in the White House for eight years, it almost always loses. Examples include the Republican loss in 2008 after eight years of George W. Bush and the Democratic loss of 2000 after eight years of Bill Clinton.

Political scientist Larry Bartels of Vanderbilt University calls this phenomenon “incumbent party fatigue.” In his statistical model for presidential elections, he calculates that the incumbent party loses almost 1 percentage point of the popular vote for every additional year it holds the White House.

Plenty of other political scientists and forecasters agree. And if that “time for a change” rule holds, it means Clinton -- or any other Democrat -- should have a hard time winning in 2016.

But not everyone agrees that the “rule” is reliable. Lynn Vavreck of UCLA, coauthor of “The Gamble,” thinks the pattern may be partly coincidental. If you look more closely at those elections, she notes, the incumbent party often performed quite well. In 2000, Al Gore actually won the popular vote, but he lost the electoral vote (and the presidency) in the Supreme Court. In 1960 and 1968, the incumbent party lost but by a margin smaller than 1 percentage point. “Those were almost ties,” Vavreck notes. Take those three examples away, and the pattern isn’t so impressive anymore.

What factor matters more? Economic growth, Vavreck and others say. If the economy is booming, voters feel good about the incumbent party. That’s how George H.W. Bush bucked the rule in 1988 after eight years of Ronald Reagan, and how Gore won the popular vote in 2000 after eight years of Clinton.

So what Democrats have to root for is clear: an economic boom in the last two years of the Obama administration, 2015 and 2016. Their only problem: That’s easier said than done.